Background

Flaxseed and flaxseed oil (or linseed oil) are rich sources of the essential fatty acid alpha-linolenic acid (ALA). In the body, some ALA is converted to omega-3 fatty acids.

Lignans are a type of plant hormone similar to estrogen. The lignan components of flaxseed (not flaxseed oil) may possess antioxidant properties and alter estrogen activity.

As a source of fiber, flaxseed (not flaxseed oil) has laxative properties. In large doses, or when taken without enough water, flaxseed may cause bowel obstruction. The effects of flaxseed on blood sugar levels are unclear.

Flaxseed oil contains only the ALA component of flaxseed and not the fiber or lignan components. Therefore, flaxseed oil may share the potential cholesterol-lowering properties of flaxseed, but not the proposed laxative or anticancer abilities.

Dosing

The below doses are based on scientific research, publications, traditional use, or expert opinion. Many herbs and supplements have not been thoroughly tested, and safety and effectiveness may not be proven. Brands may be made differently, with variable ingredients, even within the same brand. The below doses may not apply to all products. You should read product labels, and discuss doses with a qualified healthcare provider before starting therapy.

Adults (18 years and older)

General: Flaxseed oil is most often used in a liquid form, which contains approximately 7 grams of ALA and approximately 130 calories per 15 milliliters or 1 tablespoon. Flaxseed oil is available in a capsule form, which often contains 500 milligrams of ALA per 1,000 milligrams capsule (10 calories).

Whole or bruised (not ground) flaxseed may be mixed with water or juice and ingested. Generally, one tablespoon in this form may be mixed with 6-12 ounces of liquid and taken up to three times daily. Some studies have used up to 60-80 grams per kilogram of soluble flaxseed mucilage or fiber. These forms of flaxseed should not be confused with preparations of flaxseed oil.

In several studies, adults have consumed up to 50 grams of ground raw flaxseeds daily for periods not exceeding four weeks. Generally, the higher the dose, the greater the risk of gastrointestinal side effects. A dose of 50 grams of flaxseeds daily may correlate with 250 grams of flaxseed flour. In large doses, or when taken without enough water, flaxseed may cause bowel obstruction. At high temperatures, such as cooking, flaxseed oil and powder or flour will degrade.

For breast cancer, 10-25 grams of flaxseed or 5-25 grams of ground flaxseed has been taken by mouth daily for up to 16 weeks.

For breast pain (mastalgia), a muffin containing 25 grams of flaxseed has been taken by mouth daily for six months.

For constipation, 2-3 tablespoons of bulk seed mixed in 10 times the amount of water or 45 grams of bulk seed daily has been taken by mouth. Up to 15 grams of fiber from a flax fiber supplement has been taken by mouth for two weeks.

For diabetes, three capsules containing lignan (0.6 grams per capsule, which provided a total of 360 milligrams of isolated flaxseed lignan) have been taken by mouth daily for 12 weeks. Additionally, 40-50 grams of flaxseed, 32 grams of milled flaxseed, 13 grams of flaxseed oil, or 10 grams of flaxseed powder has been taken by mouth for up to 12 weeks.

For dry eye syndrome, 1-2 grams of flaxseed oil capsules have been taken by mouth daily for 180 days.

For enlarged prostate (benign prostatic hypertrophy), 300 and 600 milligrams of a flaxseed lignan extract containing 33% secoisolariciresinol diglucoside (SDG) have been taken by mouth for four months.

For exercise performance enhancement, 30 milliliters of flaxseed oil has been taken by mouth daily for 12 weeks.

For heart disease, 10-30 milliliters of flaxseed oil (containing 4.5 -13.5 grams of ALA) has been taken by mouth daily for 10-12 months.

For high blood pressure, 15-60 milliliters of flaxseed oil or three tablets containing 550 milligrams of flax extract have been taken by mouth daily for up to six months.

For high cholesterol, 20-50 grams of flaxseed (whole, ground, or defatted), flaxseed oil containing 1-38 grams of ALA, 5.2-16 grams or 60 milliliters of flaxseed oil, 200-600 milligrams of flaxseed lignan, 10 grams of flaxseed powder, flaxseed oil extract, and flaxseed-containing muffins, breads, and margarine have been used taken by mouth daily for 2-52 weeks.

For irritable bowel syndrome, 24 grams (two tablespoons) of whole flaxseed or ground flaxseed has been taken by mouth daily for four weeks. One tablespoon of whole or bruised seed mixed with 150 milliliters of liquid has reportedly been taken by mouth 2-3 times daily.

For lupus, 30 grams of flaxseed has been taken by mouth daily for four weeks.

For menopausal symptoms, 5-45 grams of flaxseed, ground flaxseed, or two 500 milligram capsules have been taken by mouth daily for up to 12 months.

For metabolic syndrome, 3-12 capsules of flaxseed oil (550 milligrams of ALA per capsule), 30 grams of flaxseed or 550 milligrams of flax extract have been taken by mouth daily for up to six months.

For obesity, 30 grams of flaxseed flour (5 grams of ALA and omega-3), 60 grams of flaxseed, a 300 milliliter flax drink, or seven tablets with flax fiber extract have been taken by mouth for up to 12 weeks. A diet of animal products from animals fed 5% linseed, as well as plant products consisting of 5 grams of extruded linseed flour, and bread with 4% extruded linseed flour, has been consumed daily for 90 days.

For osteoporosis, 40 grams of flaxseed or ground flaxseed, 30 milliliters flaxseed oil, or 550 milligrams of flax extract have been taken by mouth daily for up to 12 months.

For polycystic ovarian syndrome, six capsules of flaxseed oil containing 545 milligrams of ALA (Barleans Organic Oils, Ferndale, WA) have been taken by mouth daily for six weeks.

For premature infants, 2.2 grams of ALA has been taken by mouth daily as flax oil from week 17-27 of gestation until delivery.

For pressure ulcers, FlaxAid dressings were applied daily to the skin for 12 weeks.

For prostate cancer, a diet supplemented with 30 grams of flaxseed has been taken by mouth for at least 21 days before surgery.

For skin conditions (sensitivity), two capsules of flaxseed oil were taken with breakfast and two with dinner daily for 12 weeks. Additionally, four capsules of flaxseed oil (555.32 milligrams per capsule) have been taken by mouth daily for 12 weeks. Additionally, 30-100 grams of flaxseed flour may be mixed with warm or hot water to form a moist compress up to three times daily.

Flaxseeds have been used for foreign body removal in the eye by placing a single whole flaxseed under the eyelid and allowing the foreign body or mucus to adhere to it. This process may be unsafe, and it is suggested that a healthcare professional be consulted for removal of foreign bodies from the eye.

Children (under 18 years old)

For attention-deficit hyperactivity disorder (ADHD), flax oil with 200 milligrams of ALA content, along with 25 milligrams of vitamin C, has been taken by mouth twice daily for three months.

For bipolar disorder, dosing gradually increasing by 1-2 grams to a maximum total dose of six capsules twice daily (up to 6.5 grams of ALA) has been taken by mouth for 16 weeks.

For premature infants, a pillow filled with flaxseed on the chest for 15 minutes twice daily has been used for the first five days of life.

Evidence

These uses have been tested in humans or animals. Safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified healthcare provider.

Constipation

Good evidence suggests that flaxseed (not flaxseed oil) produces laxative effects. Loose stools have been seen in people taking flaxseed. Further research is needed to establish efficacy and dosing. Flaxseed in large doses, or when taken without enough water, may cause bowel obstruction.

C

Attention-deficit hyperactivity disorder (ADHD)

Early evidence suggests that low levels or imbalances in certain highly unsaturated fatty acids may contribute ADHD. ALA-rich nutritional supplementation in the form of flax oil may improve symptoms of ADHD. More research is needed to confirm these results.

C

Bipolar disorder

The effect of flaxseed oil in children with bipolar disorder has been examined. However, a significant effect was not reported. Further research is needed.

C

Breast cancer

It has been proposed that the lignan components of flaxseed may protect against hormone-sensitive cancers. Early evidence suggests that flaxseed supplementation may benefit the prevention or treatment of breast cancer. Additional research is needed in this area.

C

Breast pain

Flaxseed (not flaxseed oil) contains lignans that may alter estrogen activity. The hormonal effects of flaxseed may improve symptoms of breast pain. However, further research is needed before a conclusion may be drawn.

C

Clogged arteries

Flaxseed may improve clogged arteries or cardiovascular outcomes, based on antioxidant and lipid-lowering properties. n-3 polyunsaturated fatty acids and ALA may benefit individuals with heart disease. Diets rich in ALA, such as the Mediterranean diet, have improved outcomes in people with a previous heart attack. Additional research is needed in this area.

C

Diabetes

Flax has been studied for its effects on blood sugar, but reports are inconclusive. Further research is needed in this area.

C

Dry eye syndrome

Limited research suggests that flaxseed oil capsules daily may be useful in the treatment of dry eye syndrome. Additional research is needed in this area.

C

Enlarged prostate

A flaxseed lignan extract has been reported to improve urinary tract symptoms in people with benign prostatic hyperplasia (enlarged prostate). Additional well-designed trials are needed before a conclusion may be drawn.

C

Heart disease

Flaxseed may improve clogged arteries or cardiovascular outcomes, based on antioxidant and lipid-lowering properties. In humans, increased consumption of ALA may protect against stroke. However, evidence is mixed. Additional research is needed in this area.

C

High blood pressure

Early evidence suggests that higher levels of ALA in fat tissues may be associated with lower blood pressure. Flaxseed-supplemented diets have lowered blood pressure in human studies. However, future research is needed in this area.

C

High cholesterol

Flaxseed and flaxseed oil have been reported to have lipid-lowering properties. Multiple human studies on flax had mixed results on cholesterol. Additional research is needed in this area.

C

HIV/AIDS (weight gain)

Limited research suggests that ALA (derived from flax) with arginine and yeast RNA aided weight gain in people with HIV. Further research is needed before a conclusion may be drawn.

C

Irritable bowel

It has been suggested that flaxseed (not flaxseed oil) produces laxative effects. Loose stools have been observed in people taking flaxseed. Further research is needed to establish efficacy and dosing. In large doses, or when taken without enough water, flaxseed may cause bowel obstruction.

C

Lupus nephritis

Limited research suggests flaxseed may improve kidney function in people with lupus nephritis (inflamed kidney). Further research is needed before a conclusion may be drawn.

C

Menopausal symptoms

Early research suggests that flaxseed may improve menopausal symptoms, such as bone mineral density and cholesterol. However, the effects of flaxseed on menopausal symptoms are mixed. Additional research is needed.

C

Metabolic syndrome

Flaxseed has been studied for disorders of metabolic syndrome (high blood pressure, cholesterol, and diabetes) with mixed results. Trials on people with metabolic syndrome are also inconclusive. Further research is needed.

C

Obesity

Limited research exists on the effects of flaxseed in obese patients. Early research has lacked evidence of benefit in weight loss. Flaxseed has caused a reduction in hunger and an increase in fullness. Further research is needed.

C

Pneumonia (community acquired)

Limited data exists on flaxseed use for community-acquired pneumonia. Seeds from the plant have historically been used for upper respiratory infections. Further well-controlled trials are needed to confirm this conclusion.

C

Polycystic ovarian syndrome (hormonal disorder)

Flaxseed has been studied for several aspects of polycystic ovarian syndrome, including insulin resistance, obesity, and hormone changes, with mixed results. Further research is needed in this area.

C

Premature infants

It has been proposed that ALA may delay the timing of spontaneous delivery, but the available evidence lacks support for this use. The use of a flaxseed pillow in premature infants has also been studied.

C

Pressure ulcers

Flaxseed dressings on pressure ulcers have been studied. Future well-controlled trials are needed in this area.

C

Prostate cancer

There are conflicting reports on ALA and prostate cancer. Several studies suggest benefit while other studies have associated ALA with an increased risk of prostate cancer. Additional high quality studies are needed.

C

Skin conditions (sensitivity)

Seeds from the flax plant have historically been used for skin inflammation. Flaxseed oil has been applied to the skin as a salve or used for sore throat. Flaxseed oral supplementation has been studied in women with skin sensitivities. Further research is needed in this area.

D

Antioxidant

Flaxseed oil and its lignin have been found to possess antioxidant properties. Diets supplemented with flaxseed (not flaxseed oil) have been associated with an increase in cell damage. Additional research is needed.

D

Exercise performance enhancement

Limited research exists on the effects of flaxseed for improving resistance training. Taking flax oil lacked an effect on resistance training. Further research is needed.

D

Osteoporosis

Phytoestrogens, like flaxseed, have been studied for their effects on the prevention and treatment of osteoporosis. Several studies have lacked a significant effect of flaxseed on osteoporosis risk or bone mineral density. Further study is needed in this area.

Uses based on tradition or theory

The below uses are based on tradition or scientific theories. They often have not been thoroughly tested in humans, and safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified healthcare provider.

Interactions

Interactions with Drugs

General: Consumption of flaxseed (not flaxseed oil) may decrease the absorption of other drugs, vitamins, or minerals. Oral agents should be taken one hour before or two hours after flaxseed to prevent decreased absorption.

Flaxseed may lower blood sugar levels. Caution is advised when using medications that may also lower blood sugar. People taking drugs for diabetes by mouth or insulin should be monitored closely by a qualified healthcare professional, including a pharmacist. Medication adjustments may be necessary.

Flaxseed may increase the risk of bleeding when taken with drugs that increase the risk of bleeding. Some examples include aspirin, anticoagulants ("blood thinners") such as warfarin (Coumadin®) or heparin, anti-platelet drugs such as clopidogrel (Plavix®), and non-steroidal anti-inflammatory drugs such as ibuprofen (Motrin®, Advil®) or naproxen (Naprosyn®, Aleve®).

Because flaxseed contains estrogen like chemicals, the effects of other agents believed to have estrogen-like properties may be altered.

Flaxseed may also interact with agents for cancer or obesity; anti-inflammatories; cholesterol lowering agents; estrogens; laxatives; or loop diuretics.

Interactions with Herbs and Dietary Supplements

General: Consumption of flaxseed (not flaxseed oil) may decrease the absorption of other drugs, vitamins, or minerals. Oral agents should be taken one hour before or two hours after flaxseed to prevent decreased absorption.

Flaxseed may lower blood sugar levels. Caution is advised when using herbs or supplements that may also lower blood sugar. Blood glucose levels may require monitoring, and doses may need adjustment.

Flaxseed may increase the risk of bleeding when taken with herbs and supplements that are believed to increase the risk of bleeding. Multiple cases of bleeding have been reported with the use of Ginkgo biloba, and fewer cases with garlic and saw palmetto. Numerous other agents may theoretically increase the risk of bleeding, although this has not been proven in most cases.

Because flaxseed contains estrogen like chemicals, the effects of other agents believed to have estrogen-like properties may be altered.

Flaxseed may cause low blood pressure. Caution is advised in people taking herbs or supplements that lower blood pressure.

Flaxseed may also interact with anti-inflammatories, antioxidants, cholesterol lowering herbs and supplements, herbs and supplements for cancer or obesity, herbs and supplements that increase urination, laxatives, phytoestrogens, psyllium, soy, or vitamin E.

Methodology

This information is based on a systematic review of scientific literature and was peer-reviewed and edited by contributors to the Natural Standard Research Collaboration (www.naturalstandard.com).

Safety

The U.S. Food and Drug Administration does not strictly regulate herbs and supplements. There is no guarantee of strength, purity or safety of products, and effects may vary. You should always read product labels. If you have a medical condition, or are taking other drugs, herbs, or supplements, you should speak with a qualified healthcare provider before starting a new therapy. Consult a healthcare provider immediately if you experience side effects.

Allergies

Avoid with known allergy or sensitivity to flaxseed, flaxseed oil, its parts, or any other members of the Linaceae plant family.

Side Effects and Warnings

Both flaxseed and flaxseed oil are likely safe when taken by mouth in suggested doses for under four months by healthy people. A part of flaxseed, alpha-linolenic acid (ALA), has been well tolerated for up to five years as part of the Mediterranean diet. Flaxseed should be ingested with adequate fluid intake (1:10 seed: liquid is suggested). Application to the skin of the seed form or poultice is generally well tolerated.

Flaxseed or flaxseed oil is possibly safe when used for more than four months. Flaxseed or flaxseed oil is possibly safe when used in pregnant or lactating women in amounts normally consumed in food or under guidance of a practitioner.

Flaxseed may lower blood sugar levels. Caution is advised in people with diabetes or hypoglycemia, and in those taking drugs, herbs, or supplements that affect blood sugar. Blood glucose levels may need to be monitored by a qualified healthcare professional, including a pharmacist, and medication adjustments may be necessary.

Flaxseed may increase the risk of bleeding. Caution is advised in people with bleeding disorders or taking drugs that may increase the risk of bleeding. Dosing adjustments may be necessary.

Flaxseed may cause low blood pressure. Caution is advised in people taking drugs or herbs and supplements that lower blood pressure.

Use cautiously in people with prostate cancer, high triglycerides, or hypothyroidism (underactive thyroid).

Use cautiously in women with hormone-sensitive conditions or women taking estrogens. Use cautiously pregnant or lactating women. Use cautiously in people taking laxatives, furosemide, or ketoprofen.

Avoid in people with known allergy or sensitivity to flaxseed, flaxseed oil, its constituents, or any other members of the Linaceae plant family.

Avoid in people with acute or chronic diarrhea, diverticulitis (colon disorder), or inflammatory bowel disease. Avoid use in open wounds or scraped surfaces. Avoid flaxseed (not flaxseed oil) in people with narrowing of the esophagus/stomach/intestines or bowel obstruction.

Intestinal obstruction may occur when large amounts of flaxseed are ingested, or when taken without enough water or liquid (1:10 seed: liquid is suggested). Immature flaxseed seedpods may be poisonous and should not be consumed.

Pregnancy and Breastfeeding

Human evidence of medicinal use of flaxseed or flaxseed oil during pregnancy and lactation is limited.

A study reported that flaxseed oil supplementation led to a significant increase in ALA, eicosapentaenoic acid (EPA), and docosapentaenoic acid (DPA) in the breast milk. Fatty acid levels in breast milk returned to baseline one week after discontinuing supplementation.

In a survey, flax was reported to be one of the most frequently used herbal products by the pregnant women surveyed.

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